maximum outdoor wireless range

[Dragan Mickovic]

I am looking into getting AP1200 and wanted to know which external antena should I use to get the maximum outdoor wireless range? And do anybody know of a number for the wireless range? Anybody tested/experimented?

thanks

[travis-dennis_2]

Here is a link for antennas.

http://www.cisco.com/en/US/products/hw/wireless/ps469/index.html

Model AIR-ANT3338 is going to give you the most range at 25 miles@ 2mbps and 11 miles at 11mbps. Of course these and any figures are subject to environment variables and you may not be able to achieve these numbers. A site survey is the best way to go before rollout.

Hope this helps.

Please remember to rate all posts.

[scottmac]

Are you looking for a point-to-point link, or trying to cover a large area for access by clients?

Generally speaking, the factors that will give you best client coverage are antenna gain and line-of-sight. Line-of-sight can usually be enhanced with altitude. Where you have to be careful is putting a single omni antenna in the middle of a buildings roof. The building will create a downward "shadow" for clients that are close to the building.

In cases like this, it would be best to put an antenna on each side or corner of the building that feeding (at least) two access points or a single high-gain omni on a mast well above the roof.

Remember, for outside antennas, it's best to use a fiber segment connecting the APs to the rest of the LAN to prevent lightning and static damage to the LAN and attached components.

Post a good description of what you are trying to do and perhaps a more specific answer can be posted.

Good Luck

Scott

[Dragan Mickovic]

I am trying to get a maximum client coverage in a low buildings area (putting an antenna on roof of a 2 or 3 story building). Also are there any rules or regulations or permits that I need to worry about if I put a high gain antenna on 2.4Ghz range?

thanks

[scottmac]

You may have an issue with the building causing a "shadow" (close-in to the building).

You'll need either multiple access points near the edge, or a very tall mast.

As far as regulations and code: they are different from city-to-city, county-to-county, state-to-state, and country-to country. Your best bet is to check with the local building authority (where you would go to get a construction permit), maybe even ask an amateur radio operator (Ham Radio), check to see if anyone in your area specializes in that kind of work and pay them to write up an evaluation and / or recommendation.

Again, it is extremely important to make sure you're as "lightning-proof" as possible. Use a fiber link, follow the grounding codes and don't cheap out on the protection apparatus.

Also, in response to the other poster's comment about transmitting farther than you can hear: antenna gain works in both directions. Given equal power and a proper setup (cabling, couplers, connectors, etc.), if the client / receiver can hear the transmitter, the other path should be open as well.

Good Luck

Scott

[d.beaver]

Scott,

I agree with your statement about "Given equal power and a proper setup (cabling, couplers, connectors, etc.), if the client / receiver can hear the transmitter, the other path should be open as well." but I believe this is only true if the antenna gain is equal on both sides. For example, the AP and the client must both have 2.2dBi antennas for this work. If the antenna were a 5.2dBi Omni-directional antenna, and the client is still a 2.2dBi, then the access point will broadcast farther than the client can respond. Is that what you were making reference to?

Thanks.

David Beaver

[scottmac]

What I meant is: the gain for the path (on both the transmit and the receive) is exactly the same.

If the transmitting antenna (one end of the connection) is 2.2dbi and the receive antenna (the other end of the connection)is 2.2dbi, then the total path gain is effectively 4.4 dbi end-to-end, regardless of which end the transmitter or receiver is placed.

In other words, given if the client can hear the AP, the AP should be able to hear the client, given equal power. IF the AP is transmitting at 100mw, and the client is only at 50mw, then yes, the client is going to lack sufficient drive to reach the AP (but still hear the AP).

If both are fed 100mw, with a clear line-of-sight, then if the client can see the AP, then the AP should see the client.

Certainly there can be other factors (polarity, SQ, local interference, etc.) but, all things being equal, there is no difference from one to the other as far as range.

Gain is gain - the rating on the antenna refers to both transmitting gain and receiving.

FWIW

Scott

[d.beaver]

Also remember, if you are installing this for client access, you are limited to the weaker of your two antennae. In other words, the factory Cisco client card is a 2.2 dBi Omni antenna. Having a higher gain antenna on your access point will not necessarily give you a bigger coverage area. The AP's antenna will be covering a larger area, but the client is still limited to talk back to the AP by its low range.

DB

[gamccall]

erm... that's only true to an extent. Having a high-gain antenna on the AP increases not only the AP's transmit range but also its receive sensitivity; you're certainly not going to get multi-mile range with a client adapter like you would with a dish-to-dish solution, but improving your AP's antenna most definitely does increase your usable client coverage area.

[d.beaver]

Understood. I could see where the receive sensitivity is greater with a higher gain antenna, and I can see where that may give you a few feet more of reception from the client that a same gain antenna may not make use of, but it doesn't necessarily increase the coverage area of the client, and it greatly increases the coverage area of the access point. I think the biggest issue with using dissimilar gain antenna's is the security vulnerabilities you get subjected to.

For example, (in an open environment) a 5.2dBi antenna with the AP set at 100mW can broadcast a circumference of .62 miles and the client broadcasting at 100mW with a 2.2dBi antenna at best is .25 miles. So my clients range is at best .25 or .26 miles away from the access point. However, someone equipped with a LMC card and a higher gain antenna could set out at that .62 mile point and try to gain access to the AP.

That is what I worry about when deploying access points a customers environment. In keeping the gain equal on both ends, I feel I have a better idea of the edge of the AP's broadcast field and can control where that edge falls in that specific environment, aiding in the prevention of unwanted hacks.

Thanks,

Dave

[gamccall]

You're not understanding- the receive gain not only increases, it increases in the same proportion as the transmit gain. Assuming equal power on each side, then if the client can 'hear' the AP, then the AP can 'hear' the client: if the client's antenna has enough receive gain to pull in the AP's signal, then it has enough transmit gain to send a signal back, because it's the same number.

If you're concerned about security, implement EAP or WPA or 11i. Power tuning is not security- the signal doesn't hit a magical wall at .62 miles and then stop. Even with power at the lowest setting, communication can still be established from outside your intended radius if a user has a sufficiently directional antenna, unless you wrap up your building in a Faraday cage. There is no 'edge' to a broadcast field, just continuous attenuation.

[d.beaver]

"Assuming equal power on each side" would mean having the same dB antenna's and power output on each end, not a higher gain antenna on one end. I am also aware that attenuation is continuous, but it does not go on forever. It also decreases to a point that the signal is no longer recognizable by the receiving end, thus the magical wall. By recognizing this point you reduce your security factors greatly beyond EAP, WPA, or 11i.

[gamccall]

I'm sorry, but your understanding of the underlying science is incorrect.

Power is power. Gain is gain. Power is not gain. Equal power is not synonymous with equal gain.

Signal strength is a function of transmit power (i.e. wattage), transmit gain plus receive gain, and attenuation. Attenuation is always the same both ways. Transmit gain plus receive gain is always the same both ways: a+b is always equal to b+a. The only factor which can be asymmetric is transmit power.

If you have the same radio wattage on each side, then you have symmetric communications regardless of what antennas are in use. A can hear B if and only if B can hear A.

If the client's antenna does not provide enough transmit gain to successfully send data to the access point, then it's not providing enough receive gain to successfully pull in data that the access point is sending.

The only way you can have a scenario where a client can 'hear' an access point but be unable to successfully 'talk' to it, is if the client is broadcasting at a lower wattage than the AP.

Increasing antenna gain on just one side of a link will increase communication range for that link in both directions. That's the way antennas work.

-Gabriel

[1mguerreiro]

What are you doing to protect the AP1200 from the weather? Also, what are you doing to protect your inside equipment should your Antenna gets struct by lightning? Picture this: Antenna gets hit by lightning which then goes to the AP which follows the RJ45 cable to the next piece of equipment in the network. If this were an AP1400 the recommendation would have been to install a lightning resistor as well as a fiber connection between the AP and the next inline switch.

M

[scottmac]

That little (so called) lightning arrestor thingy is only good as a static drain in dry / snowy / dusty / windy environments and to bleed out some of the atmospheric charge present when thunder storms are within ~5-20 mile from the location.

Wind & dust or snow can cause a static charge on the exposed components ... the "arrestor" will bleed those charges off to prevent a critical buildup.

It is of absolutely no help (even with perfect installations) for a direct or nearby strike.

Lightning is a strange critter. A 3/4 inch gas popper isn't going to stop it,and ONLY if the attached grounding system is perfect (99% aren't even close) do you stand a chance of redirecting the energy.

Check out some of the books and materials available from PolyPhaser on grounding systems and you'll see what I mean.

Keep the APs inside or in an environmental compartment / enclosure, connect the APs to the LAN through a (longer is better) segment of fiber (put fiber / copper converters on each end if you have to).

Good Luck

Scott